Studies of the intrarenal circulation in patients with hypertension or renal failure are underway. Renal cortical blood flow is measured by the 133 Xenon washout technique; the renal cortical vasculature is visualized using high magnification arteriography. Patients with high, normal and low renin hypertension are under study as patients with hypertension, proteinuria and and renal failure associated with scleroderma (progressive systemic sclerosis). In the latter illness functional vascoconstriction of renal cortical vessels together with intimal lesions of interlobular vessels appear to be pathogenetic factors in the development of renal failure.